Roots: The popular legend of the Rat King including, potentially, Alan Moore's use of same in Book Two of The Ballad of Halo Jones for 2000AD. James Herbert's The Rats. Mrs Frisby and the Rats of NIMH. The Doctor refers to the Pied Piper of Hamlyn, while Tegan refers to the Rat King as "the Three Mouseketeers" - the Doctor calls it "King Rat" . The audiotape from 1958 includes a recording of a Goon Show episode. The backdrop to this story is the 1983 UK landslide election.

Technobabble: Turlough finds 'an archon feed' to the time vortex in the TARDIS to charge the sparkwire.

Double Entendres: "There you go, Matthew. It's all in the wrist action - you see?"

Continuity: Operation daylight was a WWII attempt to liberate France, based in the cliffs below Cadogan castle. Cadogan castle was to have been a nuclear bunker for the prime Minister and cabinet. Tunnels were built under the castle around the sixteenth century. The Doctor was in the tunnels forty years earlier and knows the control room (he implies that he worked alongside Churchill there.) Hundreds of years ago a plague tore through the land and plague pits for the victims were dug. Burial pits were found in the late 60s when a shopping centre was to be built on the site (it was then shifted to a reserve.) The Government, recalling the plague pits, sealed it up in the 1960s. The tunnels are to be sold to English heritage in a month's time, spurring the alleged intervention of the Urban Explorers Collective in the area.

The rats here have enlarged craniums, cauterised skin and obvious metallic subcutaneous implants. They are around the size of a small dog. 'Smart rats' were bred and enhanced with the introduction of acids, proteins and synthetic strings to their diets, intended to create "the ultimate spy", followed by other, later potential applications, including guard dogs. The superior rats spent years planning, faked the accident and evacuated nearly all personnel before sealing their tormentors in and 'augmenting' them in turn. The rats contact Nyssa telepathically, although the Doctor is sceptical. The rats are equipped with transcendental wavelength receivers - their telepathy is explained by the Doctor as 'no more than a neural wavelength broadcast from a central location."

The TARDIS' temporal calibration is now past the Twenty-first century. Its state of Temporal Grace appears to be working here, but allows Turlough to wield a broom defensively and use the sparkwire as a weapon (see: Links)

Nyssa says she's never harmed another creature in her research. Her proposed cure for Richters is prone to destabilising and degrading.

Tegan once saw a joust at a Renaissance fair in Sydney.

The Doctor says he has superior psychic defences, having held off stronger minds than the rats. He always intended to visit Cadogan castle during the signing of the treaty of the Marshes

Links: Karaktids and Helheim - Nyssa is still trying to isolate a cure for Richter's (Cobwebs) Nyssa refers to "the knights we saw in Stockbridge" (Castle of Fear) and Turlough on Samur (Heroes of Sontar) Kiss of Death. The rats mention the "snake" in Tegan's mind (Kinda, Snakedance, Cradle of the Snake) rat scientist '58' mentions the Master and Nyssa's desire for revenge (The Keeper of Traken, Logopolis) Turlough uses the sparkwire he retrieved from Purity Bay (The Whispering Forest). The Doctor mentions UNIT.

The Bottom Line: A good debut for Tony Lee, and a welcome role for Terry Molloy, who manages to turn a functional scapegoat role into something sympathetic (one day it would be nice for a misguided scientist long-having seen the error of his ways to not just sacrifice himself nobly as a matter of duty.) The historical location is well drawn, although it is a tad inconsequential as the story unfolds. Good sound design, and a creepy final scene - this is the best story of the trilogy.

THE DOCTOR AND WINSTON

The Eleventh Doctor adventure Victory of the Daleks establishes that the Doctor and Sir Winston Churchill have considerable shared history, and non-televised adventures certainly also bear witness to this.

Setting aside Terrance Dicks' Third Doctor staged version of The Ultimate Adventure for Big Finish's Sixth Doctor audio, the earliest reliable account of the Doctor and Churchill working together is likely to have been at least in the Doctor's Fourth incarnation (an earlier version is quite possible, but not yet confirmed.) In Churchill's life their earliest meeting is around June 1940, following the Dunkirk Withdrawal when the Doctor inspired the sombre future prime Minister's "their finest hour" speech and helped him along the road to fame and power (referred to in The Ultimate Adventure.) After this we can assume that the Doctor was well within the Prime Minister's confidence, advising him on policy and working alongside him in the secret tunnels and bunker below Cadogan Castle (alluded to in Rat Trap), as well as being privy to more tunnels - this time in preparation for smuggling the nation's art treasures out of the National Gallery (recalled in Energy of the Daleks.) In all instances it is conceivable the Doctor was in the same body, and possible that the pair's collaboration took place over a short period of time - perhaps as early as 1940 through to at least 1943 (forty years prior to the events of Rat Trap by the Fifth Doctor's reckoning). Indeed, the Doctor may have contained his working with Churchill to the Battle of Britain, although as Sir Winston instantly recognises the Time Lord in his Eleventh incarnation we may assume that the Doctor continued his acquaintance with Churchill in further regenerations still.